The present invention relates to novel biosurfactant compounds that are produced by Aureobasidium pullulans sp. L-3-GPY as a biosurfactant producing microorganism.
Surfactants are usually organic compounds that contain both hydrophobic groups and hydrophilic groups within a molecule, and that lower the surface tension of a liquid by modifying surface or interfacial properties. If a water phase is present, surfactants act by weakening the binding of water molecules to one another. At a concentration level known as the critical micelle concentration, surfactant molecules form a micelle structure in which hydrophobic groups are located on the outside of the structure and hydrophilic groups are located on the inside thereof. In a hydrophobic solution, such as a hydrocarbon solution, surfactants form an emulsion. Surfactants are characterized by having physical properties such as dispersibility, emulsifiability, permeability, wettability and bubble-forming capability. It has been reported that surfactants increase desorption and solubility of hydrocarbons, leading to biodegradation thereof by microorganisms (Deshpande et al., 1999. Water Res., 33, 351-360; Doong and Lei, 2003. J. Hazard Mater., 96, 15-27).
While in the past surfactants have been synthesized from oils and fats in small quantities, currently chemical surfactants have been mass-produced from coal, petroleum, and the like. Additionally, chemical surfactants are currently used in various industrial fields including electronics, construction, mechanics, printing, papers, fibers, and the like. However. chemical surfactants can be problematic for several reasons. First, they are very difficult to make due to their complex manufacturing process. Also, they threaten aquatic ecosystems because they form bubbles on the surface of water, thereby blocking necessary sunlight and oxygen, and they produce toxic inorganic phosphates from organic phosphorus added to the chemical surfactants to enhance their detergency. Further, because of their extremely low biodegradability, chemical surfactants accumulate in ecosystems, exhibiting strong toxicity, and causing serious environmental pollution. By contrast, biosurfactants produced in vivo or in vitro by microorganisms, such as yeasts, fungi or bacteria, are more eco-friendly materials compared to chemical surfactants, in that they are non-toxic and biodegradable (Lee et al, 2002. Kor. J. lifescience, 12, 745-751). Furthermore, although biosurfactants have complex chemical structures that are difficult to synthesize according to conventional methods, they are still very useful compounds that could be used for specific purposes. In addition, biosurfactants produce nearly the same effects as conventional chemical surfactants on the physical and chemical properties of a solution including surface tension reduction and temperature/pH stabilization, and thus, they are very valuable materials (Ishigami et al., 1987. Chem. Lett., 763).
Biosurfactants, like chemical surfactants, can be widely used in various industrial fields such as medicine, foods, cosmetics, cleaning materials, secondary oil recovery, pulp and papers, purification of oil-contaminated land and seawater, milk fat degradation, and the like.
Since pure water has a surface tension of 72 dyne/cm or higher, and its surface tension is decreased in the presence of surfactants, surfactant concentration and activity levels are generally determined by a decrease in the surface tension of pure water. Thus, the activity of biosurfactants produced by microorganisms can be determined by measuring the surface tension of a microorganism culture solution. Generally, it has been confirmed that if the surface tension of a microbial culture solution is lower than 40 dyne/cm, then the microorganisms produce some biosurfactants, and if the surface tension is lower than 35 dyne/cm, then the microorganisms produce biosurfactants in large quantities. Therefore, microorganism cultures that are widely used in industry are those that effect a surface tension of 30 to 35 dyne/cm. It has been reported that the microorganism strain, Bacillus subtillis, effects a surface tension of 27 to 28 dyne/cm (strongest reported surface activity) when cultured in a blood agar medium.
In addition, the Aureobasidium spp. strain has been known to produce beta-glucans. Beta-glucans a type of polysaccharide, potentially enhance cell immune function, and occur most commonly as cellulose in plants, cereal grain bran, cell walls of baker's yeast, and certain fungi, mushrooms and bacteria. Beta-glucans can activate immune function of normal human cells, suppress the proliferation and recurrence of cancer cells, decrease blood glucose and cholesterol levels, improve lipid metabolism, and prevent body fat from forming and accumulating.
However, there has been no report that an Aureobasidium pullulans strain can produce biosurfactant materials.